2003 Z4 2.5 Cooling fan high speed (Jet engine loud)

[vincethome]

Hello!
I just replaced a leaking radiator and two leaking hoses. I also replaced the cooling temp sensor in the lower hose and the relay on the fan shroud. I have a mechanical water pump which I replaced last year along with the thermostat. I have drained the block and replaced the coolant and bled the system.
When the engine warms to temp the fan comes on jet engine loud highspeed bypassing the lower speed. Ima good part changer but, not much on diagnostics. Little help please!

[BimmerBreaker]

I would install INPA if you can on an old laptop... software is free, the cable is ~$20 and then you can do a live readout of what all the sensors are reading

Usually when the fan runs full speed, it is due to a faulty lower radiator hose temp sensor (radiator outlet). Without this signal, the car doesn't really know the temp of the coolant coming out of the radiator so runs at full speed to be safe.
You said you replaced the lower hose sensor. Why was this replaced - was it faulty before hand? Preventative? Do you have the old sensor laying around anywhere? And what brand replacement sensor did you use?

These fans also don't have a low and high speed per se. They are PWM controlled and the speed is variable.

[vincethome]

The lower hose was leaking at the O-ring and the sensor was showing some moisture also, sloppy fit. I ordered the part online from eEuroparts.com $21.59 with 2 yr warranty. I do have the old sensor and they look to be exact.

[vincethome]

I would install INPA if you can on an old laptop... software is free, the cable is ~$20 and then you can do a live readout of what all the sensors are reading

Usually when the fan runs full speed, it is due to a faulty lower radiator hose temp sensor (radiator outlet). Without this signal, the car doesn't really know the temp of the coolant coming out of the radiator so runs at full speed to be safe.
You said you replaced the lower hose sensor. Why was this replaced - was it faulty before hand? Preventative? Do you have the old sensor laying around anywhere? And what brand replacement sensor did you use?

These fans also don't have a low and high speed per se. They are PWM controlled and the speed is variable.

The lower hose was leaking at the O-ring and the sensor was showing some moisture also, sloppy fit. I ordered the part online from eEuroparts.com $21.59 with 2 yr warranty. I do have the old sensor and they look to be exact. Upon closer look the part was OEM. I feel as though I have the system completely bled because after running with the front elevated and driving, I have no room to add and the bleeder overflows with the screw out. I ran it today and the fan came on normal so, I let it run a few more minutes then took a spin. Back to high fan.